PROJECT SUMMARY/ABSTRACT Low back pain (LBP) is the most frequently reported musculoskeletal problem among older adults. Unique to this age group, LBP is notably associated with a decline in mobility function. Clinicians have minimal evidence upon which to base treatment decisions for older adults with LBP due to lack of research studies directly focusing on this population. Thus, the long-term goal of this line of research is to develop and test a standardized rehabilitation approach for older adults with chronic LBP that is specifically designed to optimize mobility function by addressing pain and the unique impairments identified during the initial funding period of this grant. LBP experts have concluded that patients with LBP do not belong to one homogeneous group, but rather should be classified into subgroups that share similar clinical characteristics. Identification of clinical subgroups is the first step in the development of a comprehensive therapeutic algorithm. During the initial funding period, we explored the hypothesis that modifiable, co-existing hip impairments (pain, stiffness, weakness, motion restrictions) in older adults with a primary complaint of chronic LBP would predict poor outcomes. Ultimately, in the context of a prospective cohort study of 250 older adults with chronic LBP, we confirmed this hypothesis and identified a subgroup based upon the combined presence of elevated hip pain and global weakness of the hip musculature; further, this subgroup (>40% of the sample) was at risk for markedly worse LBP and functional outcomes over the course of 12 months. Given our robust predictive findings, we developed a hip-focused rehabilitation intervention (2x/week for 8 weeks) based on current best evidence to address the hip impairments in this subgroup. Our preliminary data from the initial testing of this intervention suggest that this LBP subgroup may have a more favorable LBP treatment response when the identified hip impairments are also addressed. Therefore, the natural next step is to refine and explore the efficacy of this hip-focused intervention for the newly identified at-risk subgroup through the conduct of a well-controlled Phase II trial. In this renewal application, we propose a multi- site, single-blinded, randomized controlled, Phase II trial of 180 older adults with chronic LBP who are classified as members of the at-risk hip-spine subgroup. We will investigate whether a hip-focused intervention warrants further investigation as a treatment approach to improve LBP-related disability and physical function (gait speed) among older adults with chronic LBP. Manual therapy will be used to address hip joint pain and progressive strengthening will address hip weakness. We will also investigate improvements in hip joint pain, hip strength and functional self- efficacy as underlying mechanisms contributing to treatment success. Successful completion of this Phase II trial will provide the critical information needed to plan a definitive trial for an a priori determined, at-risk subgroup identified in our initial funding period. This line of work has the potential to transform the rehabilitative care of older adults with chronic LBP by providing treatment that specifically focuses on the amelioration of pain with the overall goal of preventing functional decline for older adults with chronic pain.